Migraine has an estimated global prevalence of 14%, and is the third most common disease in the world. Chronic migraine is especially debilitating, and these patients have limited therapeutic options that are effective. The mechanisms that underlie the movement of migraine from an episodic to a chronic disorder are not very well characterized; and a better understanding of these processes could lead to novel therapeutic targets. Alterations in neuronal plasticity have been shown to be critical for the induction and maintenance of other chronic pain conditions. Particular attention has focused on histone deacetylases (HDAC), which decrease gene expression through chromatin condensation. However, the HDAC6 isoform is restricted to the cytosol, and does not affect chromatin acetylation. One of its primary substrates is ?-tubulin, a building block for microtubules, which are the most abundant component of the cytoskeleton. Microtubules regulate cell morphology, axonal transport, and motility. They are in a constant state of polymerization and depolymerization, and this dynamic instability is critical for cellular responsivity to its environment. Tubulin acetylation encourages flexible and stable microtubules, while tubulin deacetylation, which is induced by HDAC6, results in depolymerization and microtubule instability. Recent publications have found that HDAC6 inhibitors can effectively block neuropathic pain induced by chemotherapeutic drugs, and that this effect corresponds with increased tubulin acetylation and axonal transport. Our lab has developed a preclinical model of chronic migraine-associated pain, using the known human migraine trigger nitroglycerin. Using this model we observed decreased tubulin acetylation in the trigeminovascular complex following chronic nitroglycerin treatment. We also found that a brain penetrant HDAC6 inhibitor, could completely inhibit nitroglycerin induced chronic pain. One of the aims of this proposal is to examine which pain processing regions show altered tubulin acetylation following chronic nitroglycerin treatment, and if these regions show concomitant changes in HDAC6 activity. A further aim is to determine if chronic migraine associated pain results in changes in somatodendritic branching and axonal transport, and if these changes are altered by HDAC6 inhibition. These studies provide fundamental information on how microtubule dynamics are altered in chronic migraine, and form the basis for the development of HDAC6 inhibitors for migraine treatment.